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I found out today that if I plug my Apple EarPods into my laptop's 3.5mm jack almost all the way, but not completely in, I can listen to music where the background music plays nearly perfectly, but I can barely hear the voices. Sometimes the voices become very clear, but only for a few seconds at a time. My computer's sound is perfectly operational; if I push the connector all the way in, I get normal-sounding sound.

It didn't matter whether I listened to the left or right EarPod; they sound exactly the same (to the limits of my perception -- but then again, I can't tell the difference between the left and right channels of audio anyway).

I was rather intrigued by this phenomenon, so I did some experimenting. I found some YouTube videos that played 20 Hz - 20 kHz tones in succession, and I couldn't hear anything. This was rather surprising to me, because music is just a Fourier series of pure sinusoids, and our hearing's bandwidth is limited to the range covered by the test.

I then hypothesized that I couldn't hear the test audio because the test video played the same thing for both left and right channels. Using a virtual audio cable, I changed the audio to 1 channel 24-bit audio, and sure enough, I couldn't hear anything in the music either.

On a limb, I decided to subtract the left channel from the right channel and listen to it. I followed the answer here, and generated a .wav with the two channels subtracted. It sounds exactly the same (with the headphones plugged all the way in) as what I heard with the connector not all the way in.

Why would this particular connection cause the left and right channels to be subtracted? I've built op-amp based voltage subtractors before, but I fail to see how a partly disconnected 3.5mm jack could emulate a voltage subtractor.

This is what my jack looks like. Normally, the white part is flush with the side of my computer.

picture of jack

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Cool question. This is simply due to the fact that the "tip" of the plug is shared between left and right. This is universal to all headphones, I believe. Basically what you're hearing is just the right side of the stereo signal, but it's in mono, so you're hearing it through both speakers.

  • I sometimes listen to my headphones with only the right side in, and it doesn't sound like the subtracted signal. It just sounds flatter because there's no stereo sound. The sound that I hear sounds exactly like someone subtracted R from L, not just one of the channels. – John Adams Nov 29 '18 at 22:36
  • It could be due to the fact that apple uses a proprietary plug/jack. It may have a different architecture and in your case you may well be hearing something different. Either way it sounds like probably some amalgamation of the stereo signal coming through in mono. – Brian Wright Nov 29 '18 at 22:52

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